Weather Prediction Center issues Mesoscale Precipitation Discussion #929 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE
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AWUS01 KWNH 261659
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MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-262256-
Mesoscale Precipitation Discussion 0929
NWS Weather Prediction Center College Park MD
1258 PM EDT Mon Aug 26 2024
Areas affected...New England
Concerning...Heavy rainfall...Flash flooding possible
Valid 261656Z - 262256Z
SUMMARY...Showers and thunderstorms rounding the western periphery
of an upper level low may briefly contain rainfall rates around
2"/hr and lead to localized flash flooding mostly in urbanized
locations and sensitive topography.
DISCUSSION...Recent satellite imagery from GOES-East depicts a
well-defined upper low sitting off the New England coast and over
the Gulf of Maine. Radar trends also show developing showers and
thunderstorms rotating around this low and exhibiting
south-southeast storm motions, while some storms remain somewhat
tied to the interior elevated ranges (Greens, Whites, and
Berkshires). PWs of 1.2-1.4" span much of New England per SPC's
mesoanalysis web page, which is supported by the 12z sounding out
of GYX. These moisture values are slightly above climatology, but
not considered anomalous. Meanwhile, steep low to mid-level lapse
rates (highest in southern New England) along with sufficient
instability will be the driving factor in supporting continued and
further development of convection through the afternoon hours that
could produce intense rainfall rates.
Recent 12z CAMs and HREF guidance depicts isolated maximum
rainfall amounts of 1-3", which would approach 3-hr FFGs in the
region if realized. Additionally, an instability gradient setup
near RI will support a focus in convection later this afternoon
(around 21z per the 15z HRRR). This region is reflected in HREF
neighborhood probabilities in having the greatest potential for
amounts over 3" (20-30%). Stronger northerly flow aloft compared
to weak surface winds may support a period of training if updrafts
can become strong enough during the 19-21z time frame. Given the
urban regions in the area flash flooding is more likely here, but
overall the threat across New England is for localized impacts.
Snell
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...ALY...BOX...BTV...GYX...OKX...
ATTN...RFC...NERFC...NWC...
LAT...LON 45107054 44706961 44016951 43217018 42537026
41896988 41497003 41277058 41177137 41287228
41627288 42147313 42887314 43787288 44447234
44957146
Source: Weather Prediction Center issues Mesoscale Precipitation Discussion #929 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE (https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=929&yr=2024)
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